Eco-friendly vehicles have been actively developed due to the exhaustion of oil energy resources and reinforced environment regulations around the world. Thus, vehicle manufacturers have been focusing on development of core technology related thereto. Accordingly, researches for reducing fuel cost and exhaust gas through improvement in fuel efficiency have been consistently conducted, particularly in improving fuel efficiency in commercial vehicles with the high use rate of oil.
In general, an electro hydraulic power steering (EHPS) system and a hydraulic idle stop and go (ISG) system are used for the fuel efficiency improvement.
The EHPS system uses a hydraulic pump which is powered by 24 volt power, instead of using an engine mount type mechanical power steering pump which runs continuously. Accordingly, the EHPS system stops the pump in a case where steering is unnecessary and adjusts the operation of the pump depending on the situation, thereby reducing unnecessary power consumption and improving fuel efficiency.
The hydraulic ISG system includes a hydraulic motor, a hydraulic pump, valves, an accumulator, etc. The hydraulic ISG system is a system which stops an engine when a vehicle stops, e.g. due to traffic lights or while passengers get into and out of the vehicle, and starts the engine using hydraulic pressure accumulated in the accumulator when the vehicle starts. A commercial hybrid bus currently utilizes an ISG function using a drive motor. However, it takes a relatively long period of time to operate an engine when the bus starts again. On the other hand, the hydraulic ISG system is a system which resolves the problem of a commercial hybrid vehicle, and is applicable to general vehicles.
However, when the above two systems are mounted in the vehicle in order to improve fuel efficiency in the prior art, it is difficult to secure a mounting space because of a large number of parts.